This invention relates generally to a circuit which can control MOS transistor current precisely. The circuit utilizes bipolar and CMOS devices for generating a CMOS gate-controlling voltage, which varies favorably with temperature, power supply voltage, and process corners, so as to yield a well-controlled CMOS current.
Conventional bipolar regulator circuits, such as bandgap regulators employing only bipolar transistors are generally well known in the prior art and can provide a very good reference voltage. The major defects of these prior art circuits is that bipolar technology is very expensive and requires higher amounts of power for operation in circuits. Thus, bipolar technology is not as popular as CMOS technology. Circuits employing CMOS technology are much easier to manufacture and utilize much less power than the bipolar ones. However, CMOS circuits have the inherent problem of being unable to provide a precise control of voltage level and current. Accordingly, the voltage and/or current levels in CMOS circuits can change drastically due to temperature, supply voltage, or process variations.
It would therefore be desirable to provide a merged or composite bipolar/CMOS regulator circuit which combines the advantages of the bipolar transistor and CMOS transistor technologies together. As a result, bipolar transistors and CMOS transistors are merged or are arranged in a common semiconductor substrate in order to form an integrated circuit regulator device which can give a precise control of voltage level and CMOS current and can be manufactured at a relatively low cost, but yet provides a much improved performance.